Russian President Vladimir Putin warned countries in the west against provoking a war with Russia, and raised the spectre of nuclear war as he defied condemnation from the international community over Russian incursions into Ukraine.

Speaking to a group of young Russians attending the Seliger 2014 National Youth Forum, Putin said that he thinks "no one is thinking of unleashing a large-scale conflict with Russia."

"I want to remind you that Russia is one of the leading nuclear powers," the Russian leader said.

This is first time since the Cold War that any Russian leader has ever directly mentioned its nuclear capability in relation to conflict. Putin is being widely criticized for brazenly putting his hand in the Ukraine disturbances and ordering Russian units into Ukraine.

Speaking at the youth forum held just outside Moscow, Putin further underlined that although Russia will not be drawn into large-scale conflicts, its partners need to understand that it is better not to provoke Russia.

Putin also explained Russia's decision to annex the Crimean Peninsula in March, saying it was important for Russia to come to the aid of the largely Russian-speaking population and defend it against Ukrainian government aggression.

As reported by Russia's state news agency Ria Novosti, Putin declared that Russia will continue to build its nuclear potential to ensure its own security, as it continues to strengthen and modernize its armed forces.

Putin's government is currently implementing an ambitious rearmament program that seeks to arm at least 30 percent of the Russian military with modern weaponry by 2020. The program costs about 20 million ruble (US$640 billion.

"This is not to threaten anyone, but to feel secure, feel calm, it gives us the ability to realize those plans that we have in the economic and social spheres," Putin stated before the Russian youth forum.

utin made his remarks as European leaders prepare to gather Saturday for an emergency summit to discuss further sanctions on Moscow, after NATO confirmed more than 1,000 regular Russian troops appeared in eastern Ukraine.